In recent years, a flat panel detector (to be referred to as an FPD hereinafter) has been put into practical use, which accumulates X-rays as a charge signal, converts it into a digital signal, and provides a diagnostic image. Such an X-ray imaging apparatus is configured to execute imaging by synchronizing X-ray irradiation of an X-ray generation apparatus and an imaging operation of the FPD.
There are also many market requirements for replacing the film or imaging plate portion of an existing modality with an FPD. When replacing the imaging unit of an existing modality with an FPD, it may be difficult to build an interface to synchronize the X-ray generation apparatus with the FPD. PTL 1 proposes an FPD that detects X-ray irradiation on the FPD side and automatically starts the accumulation operation without providing the interface between the X-ray generation apparatus and the FPD.
However, in the case in which X-ray irradiation is automatically detected on the FPD side to start the accumulation operation, X-ray irradiation needs to be performed to some extent until the FPD detects X-rays and starts the accumulation operation, and a reset operation is performed during this time. For this reason, charges accumulated by X-rays to irradiate from the start of actual X-ray irradiation to the start of the accumulation operation upon detecting the X-rays are removed. The removed charges cannot contribute to output values. Hence, even if the incident X-ray amount is the same, the output value changes between a pixel whose X-ray information is lost upon charge removal (this pixel will be referred to as an X-ray deficiency pixel hereinafter) and a pixel from which charges are not removed (this pixel will be referred to as an X-ray non-deficiency pixel hereinafter).
For example, in PTL 1, the reset operation at the time of X-ray detection is performed for every other line. Since the reset operation is performed alternately for even-numbered lines and odd-numbered lines on a frame basis, charge removal is performed for every other line from X-ray irradiation to the start of the accumulation operation. As a result, a line from which charges are removed (this line will be referred to as an X-ray deficiency line hereinafter) and a line without charge removal (this line will be referred to as an X-ray non-deficiency line hereinafter) alternately occur, and the output value difference between the lines appears as a stripe pattern on the image. Note that concerning this problem, PTL 1 discloses a method of discarding the data of X-ray deficiency lines as defects and correcting them by linear interpolation of peripheral pixels.
As a method other than that described above, there has recently been proposed a method of obtaining the X-ray deficiency ratio of an X-ray deficiency line based on an X-ray non-deficiency line adjacent to the X-ray deficiency line and digitally amplifying the output value in accordance with the deficiency ratio. This method can effectively use the output value of an X-ray deficiency line and therefore obtain a more appropriate correction result, as compared to the method of discarding the information of an X-ray deficiency line as a defect.